An image forming apparatus such as a copy machine, a printer and a multifunction printer is classified into an ink-jet type, an electro-photographic type and a thermal transfer type according to an image forming method. In the electro-photographic image forming apparatus, an image is formed on a printing medium through a series of processes such as charging, exposing, developing, transferring and fixing.
A conventional electro-photographic image forming apparatus includes a cartridge assembly in which a drum unit and a developing unit are integrally formed, wherein the drum unit has a photosensitive drum, a charging roller, transfer roller so on, and the developing unit accommodates a developer therein and has a developing roller and a supply roller.
Here, the cartridge assembly has the developer comprised of toner and carrier for a printing operation. The developer should be replenished or replaced due to consumption of the toner by the printing operation.
Formerly, the replenishment or replacement of the developer was performed by collecting and discharging a waste developer, i.e., waste toner and waste carrier at the same time and then replenishing a new developer. However, in such a developer replenishing or replacing method, a large amount of the developer is abandoned, and a waste developer receiving part is required separately.
In Japanese Patent Publication No. 1993-66659 (Patent document 1), there is disclosed an image forming apparatus in which the toner is collected and reused in consideration of a conventional developer consumption. Patent document 1 discloses a process cartridge in which a waste toner tank is integrally installed at a photosensitive drum, and a discharging system for collecting the waste toner in the waste toner tank into a developing machine is installed.
Meanwhile, in Japanese Patent Publication No. 2001-194908 (Patent document 2), there is disclosed an image forming apparatus in which the toner is collected and reused, and a supply amount of the carrier is controlled.
However, in case of the patent documents, the collected toner contains a foreign substance or paper dust generated from printing paper, and the paper dust or the foreign substance contained in the waste toner is introduced into the developing machine, while the waste toner is recycled, and has a bad influence on image quality. Therefore, there is a problem in that a life space of a cartridge having a waste toner recycling structure is shortened.